Evaluation of pliable bioresorbable, elastomeric aortic valve prostheses in sheep during 12 months post implantation.

Pliable microfibrous, bioresorbable elastomeric heart valve prostheses are investigated in search of sustainable heart valve replacement. These cell-free implants recruit cells and trigger tissue formation on the valves in situ. Our aim is to investigate the behaviour of these heart valve prostheses when exposed to the high-pressure circulation. We conducted a 12-month follow-up study in sheep to evaluate the in vivo functionality and neo-tissue formation of these valves in the aortic position. All valves remained free from endocarditis, thrombotic complications and macroscopic calcifications. Cell colonisation in the leaflets was mainly restricted to the hinge area, while resorption of synthetic fibers was limited. Most valves were pliable and structurally intact (10/15), however, other valves (5/15) showed cusp thickening, retraction or holes in the leaflets. Further research is needed to assess whether in-situ heart valve tissue engineering in the aortic position is possible or whether non-resorbable synthetic pliable prostheses are preferred.

Feasibility of electroporation for the creation of pulmonary vein ostial lesions.

INTRODUCTION: There is an obvious need for a better energy source for pulmonary vein (PV) antrum isolation. OBJECTIVE: We investigated the feasibility and safety of electroporation for the creation of PV ostial lesions. METHODS: After transseptal puncture, a custom 7F decapolar 20 mm circular ablation catheter was placed in the PV ostia of 10 pigs. Ablation was performed with a nonarcing, 200 J application delivered between the catheter and an indifferent patch electrode on the lower back. A single pulse was applied for each catheter position, with a maximum of 4 per ostium. Local PV electrogram amplitude and stimulation threshold were measured at multiple locations in both ostia before and directly after ablation, and after 3 weeks survival, using a regular 4 mm mapping catheter. All PV ostia were sectioned, stained, and histologically investigated. RESULTS: The 3-week survival period was uneventful. PV ostial electrogram amplitude decreased and stimulation threshold increased significantly in most ostia. PV angiograms did not show any stenosis during this short follow-up. Histologically, up to 3.5-mm-deep lesions were found. CONCLUSION: Data suggest that electroporation can safely be used to create lesions in a sensitive environment like PV ostia.

In-vivo validation of a new non-invasive continuous ventricular stroke volume monitoring system in an animal model.

INTRODUCTION: Recently, a non-invasive, continuous ventricular stroke volume monitoring system using skin electrodes has been developed. In contrast to impedance-based methods, the new technique (ventricular field recognition) enables measurement of changes in ventricular volume. A prototype using this new method was built (the hemologic cardiac profiler, HCP) and validated against a reference method in a pig model during variations in cardiac output. METHODS: In six Dalland pigs, cardiac output was simultaneously measured with the HCP (CO-HCP), and an invasive ultrasonic flow-probe around the ascending aorta (CO-FP). Variations in CO were achieved by change in ventricular loading conditions, cardiac pacing, and dobutamine administration. Data were analysed according to Bland-Altman analysis and Pearson's correlation. RESULTS: Pearson's correlation between the CO-HCP and the CO-FP was r = 0.978. Bland-Altman analysis showed a bias of - 0.114 L/minute, and a variability of the bias (2 standard deviations, 2SD) of 0.55 L/minute. CONCLUSIONS: The results of the present study demonstrate that CO-HCP is comparable to CO-FP in an animal model of cardiac output measurements during a wide variation of CO. Therefore, the HCP has the potential to become a clinical applicable cardiac output monitor.

Strategies to Improve Survival from Surgery for Heart Valve Implantation in Sheep.

Sheep are a commonly used and validated model for cardiovascular research and, more specifically, for heart valve research. Implanting a heart valve on the arrested heart in sheep is complex and is often complicated by difficulties in restarting the heart, causing significant on-table mortality. Therefore, optimal cardioprotective management during heart valve implantation in sheep is essential. However, little is known about successful cardioprotective management techniques in sheep. This article reports our experience in the cardioprotective management of 20 female sheep that underwent surgical aortic valve replacement with a stented tissue-engineered heart valve prosthesis. During this series of experiments, we modified our cardioprotection protocol to improve survival. We emphasize the importance of total body hypothermia and external cooling of the heart. Furthermore, we recommend repeated cardioplegia administration at 20 min intervals during surgery, with the final dosage of cardioplegia given immediately before the de-clamping of the aorta. To reduce the number of defibrillator shocks during a state of ventricular fibrillation (VF), we have learned to restart the heart by reclamping the aorta, administering cardioplegia until cardiac arrest, and de-clamping the aorta thereafter. Despite these encouraging results, more research is needed to finalize a protocol for this procedure.

The early days of vascular and heart valve prostheses: a historical review.

This surgical heritage article provides a historical overview of the most important early advances of vascular- and valvular surgery, that lead to the development of currently used vascular- and valvular prostheses and materials. The first writings describing techniques in vascular surgery mainly focussed on hemorrhage control and date from around 1600 B.C. The strategy of vessel ligation was first mentioned in Western literature around 200 B.C. In the 18th century, techniques of ligation were expanded towards attempts of vessel restoration. The first artificial vascular prosthesis was made in 1894. From this time on, vascular prostheses were used in animal experiments and around 1900 for the first time in humans. More than 60 years later, in 1952, the first mechanical heart valve prosthesis was implanted. Four years later, the first successful biological heart valve implantation followed. In 2000, a transcatheter heart valve was successfully implanted in a human for the first time. Over time, procedures and techniques became more efficient and effective. This led to new developments, such as the manufacturing of a tissue engineered blood vessel in 1986. Nowadays, dozens of different valve prostheses have been devised, both mechanical and biological. Still, no ideal model of vascular and heart valve prosthesis exists.

Failure of decellularized porcine small intestinal submucosa as a heart valved conduit.

OBJECTIVE: Decellularized extracellular matrix made from porcine small intestinal submucosa, commercially available as CorMatrix (CorMatrix Cardiovascular, Inc, Roswell, Ga) is used off-label to reconstruct heart valves. Recently, surgeons experienced failures and words of caution were raised. The aim of this study was to evaluate decellularized porcine small intestinal submucosa as right-sided heart valved conduit in a xenogeneic animal model. METHODS: A pulmonary valve replacement was performed with custom-made valved conduits in 10 lambs and 10 sheep (1 month [3 lambs and 3 sheep], 3 months [3 lambs and 3 sheep], 6 months [4 lambs and 4 sheep]). Valve function was assessed after implantation and before the animal was put to death. Explanted conduits were inspected macroscopically and analyzed using immunohistochemistry and scanning electron microscopy. They also underwent mechanical testing and testing for biochemical composition. RESULTS: All valved conduits were successfully implanted. Five sheep and 2 lambs died due to congestive heart failure within 2 months after surgery. In the animals that died, the valve leaflets were thickened with signs of inflammation (endocarditis in 4). Five sheep and 8 lambs (1 month: 6 out of 6 animals, 3 months: 4 out of 6 animals, 6 months: 3 out of 8 animals) survived planned follow-up. At the time they were put to death, 5 lambs had significant pulmonary stenosis and 1 sheep showed severe regurgitation. A well-functioning valve was seen in 4 sheep and 3 lambs for up to 3 months. These leaflets showed limited signs of remodeling. CONCLUSIONS: Fifty percent of sheep and 20% of lambs died due to valve failure before the planned follow-up period was complete. A well-functioning valve was seen in 35% of animals, albeit with limited signs of tissue remodeling at ≤3 months after implantation. Further analysis is needed to understand the disturbing dichotomous outcome before clinical application can be advised.

Added Value of Interactive 3-D Stereo Vision Echocardiography in the Heart Valve Team: A Post Hoc Analysis for Optimal Decision Making in Patients With Mitral Valve Regurgitation.

OBJECTIVE: We assessed the added value of advanced echocardiography post hoc analysis for optimal decision-making in the Heart Valve Team (HVT) using an interactive, dynamic, live visualization system with true three-dimensional (3-D) stereo vision. METHODS: HVT scrutinized the incremental value of 3 consecutive methods of presentation of full-volume echocardiographic data sets in terms of diagnosis and possibility of repair in 11 selected patients having mitral regurgitation (MR)(Table 1). The questionnaire investigated consecutively (a) standard two-dimensional (2-D) transesophageal echocardiography, (b) single-beat 3-D zoom of the surgical view of the mitral valve, and (c) advanced 3-D volumetric rendering technology (Personal Space Station, Vesalius 3D software, PS-Medtech, Netherlands). RESULTS: In 4 of 11 reviews (36%), single-beat 3-D zoom had additional value over 2-D echocardiography in terms of mechanism/adjustments or adjustment of confirmation of diagnosis. Single-beat 3-D zoom had no additional value over 2-D echocardiography in terms of proposal/probability of repair. In 7 out of 11 (64%) reviews, true stereo 3-D visualization had additional value in terms of mechanism of pathology compared to 2-D and 3-D zoom and in 5 out of 11 (45%) reviews in confirmation of diagnosis. In 3 out of 11 (27%) reviews, true stereo 3-D visualization had additional value in terms of proposal of repair and in 4 of 11 (36%) in probability of repair over 2-D and 3-D zoom. CONCLUSIONS: Advanced easy-to-use true 3-D echocardiography limited differences in interpretation and strengthened the confidence in understanding the mechanisms and suitability for repair of mitral valve regurgitation, typically in more complex valve pathology.

In Situ Remodeling Overrules Bioinspired Scaffold Architecture of Supramolecular Elastomeric Tissue-Engineered Heart Valves.

In situ tissue engineering that uses resorbable synthetic heart valve scaffolds is an affordable and practical approach for heart valve replacement; therefore, it is attractive for clinical use. This study showed no consistent collagen organization in the predefined direction of electrospun scaffolds made from a resorbable supramolecular elastomer with random or circumferentially aligned fibers, after 12 months of implantation in sheep. These unexpected findings and the observed intervalvular variability highlight the need for a mechanistic understanding of the long-term in situ remodeling processes in large animal models to improve predictability of outcome toward robust and safe clinical application.

High-frequency epicardial ultrasound: review of a multipurpose intraoperative tool for coronary surgery.

BACKGROUND: In open-chest coronary artery bypass grafting (CABG), the surgeon faces several intraoperative challenges: (1) to locate the target coronary artery, (2) to select the optimal anastomotic site, and (3) to assess the quality of the graft and distal anastomosis. Endoscopically, these three diagnostic aims are particularly challenging. METHODS: We reviewed the literature on the intraoperative application of high-frequency (6.5-15 MHz) epicardial ultrasound (ECUS) in CABG to aid in these challenges. RESULTS: Overall, ECUS was used in 628 patients to visualize and assess 912 (segments of) coronary arteries, as well as 418 grafts and distal anastomoses. In 96 cases, ECUS successfully located a coronary artery that was buried in the epicardial and/or myocardial tissue. In 37/155 (24%) imaged anastomotic sites, an alternative site free of pathology was selected. For quality assessment of the coronary anastomosis, experimental validation of ECUS included 218 anastomoses in ex vivo and animal models. ECUS showed high sensitivity (0.98) and specificity (1.00) for detection of anastomotic construction errors in 120 ex vivo anastomoses. In 418 grafts and distal anastomoses evaluated in patients, irregularities leading to revision were detected in 8 (1.9%) anastomoses and minor irregularities in an additional 23 (5.5%) anastomoses. However, little is known about the effect on long-term patency of specific anastomotic abnormalities revealed by ECUS. Scanning of arteries and anastomoses required several minutes. Current size ultrasound probes allowed successful experimental robot-assisted endoscopic application of ECUS. CONCLUSIONS: CABG may be facilitated and improved in several ways by intraoperative high-frequency epicardial ultrasound scanning. Totally endoscopic CABG may benefit from ultrasound diagnostics in particular.

Cyclooxygenase-2 inhibition increases mortality, enhances left ventricular remodeling, and impairs systolic function after myocardial infarction in the pig.

BACKGROUND: Cyclooxygenase (COX)-2 expression in the heart increases after myocardial infarction (MI). In murine models of MI, COX-2 inhibition preserves left ventricular dimensions and function. We studied the effect of selective COX-2 inhibition on left ventricular remodeling and function after MI in a pig model. METHODS AND RESULTS: Twenty-two pigs were assigned to COX-2 inhibition with a COX-2 inhibitor (COX-2i; celecoxib 400 mg twice daily; n=14) or a control group (n=8). MI was induced by left circumflex coronary artery ligation, and the animals were euthanized 6 weeks later. Cardiac dimensions and function were assessed with echocardiography and conductance catheters. Infarct size and collagen density were analyzed with triphenyltetrazolium chloride staining and picrosirius red staining, respectively. COX-2 inhibition increased mortality compared with controls (50% versus 0%, P=0.022), whereas infarct size was similar (13.1+/-0.7% versus 14.1+/-0.1%, P=0.536). The decrease in thickness of the infarcted myocardial wall was more pronounced in the COX-2i group (60.6+/-9.6% versus 36.2+/-5.7%, P=0.001). End-diastolic volume was higher in the COX-2i group (133.9+/-33.5 versus 91.1+/-24.0 mL; P=0.021), as was the end-systolic volume at 100 mm Hg (81.7+/-27.8 versus 56.3+/-21.1 mL; P=0.037), which indicates that systolic function was more severely impaired. Infarct collagen density was lower after COX-2i treatment (25.3+/-3.9 versus 56.1+/-23.8 gray value/mm2; P=0.005). CONCLUSIONS: In pigs, COX-2 inhibition after MI is associated with increased mortality, enhanced left ventricular remodeling, and impaired systolic function, probably due to decreased infarct collagen fiber density.

S2 connector versus suture: distal coronary anastomosis remodeling, patency, and function in the pig.

BACKGROUND: Anastomotic connectors could be the key to less invasive bypass surgery, including endoscopic procedures, but equivalence to conventional suturing needs to be established. A novel distal coronary connector was tested pre-clinically for safety and efficacy in comparison to conventional suturing. METHODS AND RESULTS: Left internal thoracic to left anterior descending coronary artery bypasses were constructed off-pump in 35 pigs (73+/-8 kg). An intraluminal metal connector (S2AS) was used in 21 and conventional suturing in 14 animals. S2AS anastomosis construction was easier achieved in one-fourth of the conventional construction time (3.7+/-0.7 versus 16.5+/-2.6 minutes; P<0.001). Acute patency tended to be better (P=0.15). All anastomoses were evaluated intraoperatively, and subgroups at 90 and at 180 days. Patency was 100%. An effective remodeling response was observed in all groups, resulting in unobstructed anastomoses with excellent hemodynamic performance (fractional flow reserve > or = 0.93 at 180 days). At 6 months, the noncompliant connector was covered with stabilized neointima that was thinner than found on the suture line (0.10+/-0.04 versus 0.31+/-0.13 mm; P=0.01). The connector induced less lumen loss (-0.6+/-6.5 versus 21.6+/-19%; P=0.03). The initial side-to-side configuration had remodeled to an end-to-side shape as intended. CONCLUSIONS: In the porcine model, the connector rapidly and consistently produced high-quality anastomoses that fully met current standards on patency and function. Unconventional aspects like a noncompliant intraluminal ring and a side-to-side to end-to-side converted configuration did not interfere with favorable anastomosis remodeling. These findings shed a new light on the anatomical prerequisites for anastomosis patency.

Flexible mechanoprosthesis made from woven ultra-high-molecular-weight polyethylene fibres: proof of concept in a chronic sheep model.

OBJECTIVES: Ultra-high-molecular-weight polyethylene (UHMWPE) fibres are flexible, have high tensile strength, and platelet and bacterial adhesion is low. Therefore, UHMWPE may overcome limitations of current mechanical valves and bioprostheses. In this study, the biocompatibility and functionality of prototype handmade stented valves from woven UHMWPE (U-valve) was assessed in a chronic sheep model with acetylsalicylic acid monotherapy. METHODS: Native pulmonary valves of 23 sheep were replaced by U-valves (n = 18) or Perimount bovine bioprostheses (reference group, n = 5). Sheep received 80 mg of acetylsalicylic acid daily. Follow-up was conducted at 1 week (n = 4), 1 month (n = 5), 3 months (n = 5) and 6 months (n = 4) in the U-valve group and at 3 months (n = 2) and 6 months (n = 3) in the reference group. Epicardial echocardiography and histology were used to assess valve function and tissue deposition, respectively. RESULTS: Seventeen U-valve sheep (94%) and 3 reference sheep (60%) survived the perioperative period. One reference valve sheep was sacrificed after 4 months because of congestive heart failure. At explantation, all U-valves were intact without leaflet tearing. Up to 3 months, U-valves were flexible and free of stenosis. Regurgitation was mostly mild though gradually increasing; histology showed minimal connective tissue near the leaflet base and sparse calcification. At 6 months, connective tissue was diffusely observed on the leaflets with retraction and consecutive regurgitation and leaflet thickening. CONCLUSIONS: Valves made from UHMWPE fibres demonstrated early feasibility in the pulmonary valve position with reasonably good haemodynamics and intact valve materials up to 6 months. Gradual leaflet thickening and retraction were observed after 3 months due to connective tissue overgrowth.

Myocardial blood supply by left ventricle-to-coronary artery channel: an old idea revisited.

Coronary artery disease is one of the most important causes of death in Western society. Attempts to revascularize the coronary artery by myocardial retroperfusion, direct revascularization from the left ventricle, and bypass surgery have finally led to percutaneous transluminal coronary angioplasty (PTCA) and coronary artery bypass grafting (CABG) as standard treatment for coronary artery disease. Direct revascularization from the left ventricle has already been studied in the late 1960s, but the idea was rejected because of a decrease in flow in combination with a failure of myocardial function. Recently, a left ventricle-to-coronary artery (LV-CA) stent has renewed interest as an alternative procedure when PTCA and CABG are no option. Animal studies showed a change in flow pattern from diastolic coronary inflow at baseline to systolic coronary inflow followed by diastolic regurgitive flow during direct ventricular sourcing, resulting in a coronary flow of 50-75% of baseline flow. Global myocardial function decreased in the same extent as the coronary flow suggesting perfusion-contraction matching. In a recent pilot study in the anaesthetized pig, direct revascularization after acute proximal coronary ligation resulted in sufficient blood supply to the outer layers of the myocardium, however, in the inner layers a metabolic disbalance occurred. Incorporation of a valve-like mechanism to minimize the diastolic regurgitive flow may be necessary to improve the performance of the LV-CA stent. In addition, further research should be done in chronic ischemic animal models in which the effect of the collateral circulation on myocardial perfusion and performance is an important issue.

Endoscopic exposure and stabilization of posterior and inferior branches using the endo-starfish cardiac positioner and the endo-octopus stabilizer for closed-chest beating heart multivessel CABG: hemodynamic changes in the pig.

BACKGROUND: Closed-chest, off-pump, multivessel CABG requires modified instruments to expose and stabilize posterior and inferior coronary branches. Using three new prototype devices, we explored the feasibility of endoscopic bypass grafting on these branches and assessed cardiac function during cardiac displacement. METHODS: Eight pigs (75 to 85 kg) were instrumented for hemodynamics and paced at 80 to 100 bpm. After closure of the sternotomy wound, the Da Vinci endoscope was inserted subxiphoidally. A sternal hook was used to hoist the sternum ventrally by 5 cm. The articulating EndoStarfish cardiac positioner was placed through a trocar (Ø12 mm). The positioner was fixed to the apex using -400 mm Hg suction and the heart was displaced anteriorly to 90 degrees. In 12 other pigs (75 to 85 kg), both internal mammary arteries (IMA) were harvested and the sternal wound was closed. Five trocar ports were placed for instrumentation (Ø12 mm, two in left chest, two in right chest, and one subxiphoidally). For coronary stabilization, a novel deployable EndoOctopus cardiac stabilizer was employed (suction -400 mm Hg). The Da Vinci robot-telemanipulator system was used for endoscopic grafting of the left and right IMA on posterior and inferior branches (16 anastomoses). RESULTS: When circumflex arteries were fully exposed and accessible for coronary surgery, stroke volume decreased by 18%+/-3 versus baseline (P=0.02) and mean arterial pressure decreased by 27%+/-6 (P=0.001). Additional 10 degrees Trendelenburg head-down positioning normalized stroke volume and arterial pressure. In the displaced heart, obtuse marginal branches (OM) and the ramus descending posterior (RDP) of the right coronary artery became fully exposed with a mean arterial pressure >70 mm Hg during grafting. No accidental detachment occurred. Coronary target motion was restrained to approximately 1x1 mm. In two test cases, five sham distal anastomoses were created (grafts sewn to epicardium, left IMA to OM2 jump to OM3, right IMA to RDP, and composite graft from left IMA jump to diagonal branch). In 10 animals, 16 successfully completed anastomoses to RPD and OM branches of Ø1.75 to 2.5 mm required 25 to 60 minutes each to construct. At sacrifice, all anastomoses were patent. CONCLUSIONS: In the closed-chest pig in Trendelenburg position and during lifting of the sternum, the EndoStarfish and EndoOctopus enabled IMA grafting of posterior and inferior branches on the beating heart without mean arterial pressure dropping below 70 mm Hg.

Detection of construction errors in ex vivo coronary artery anastomoses by 13-MHz epicardial ultrasonography.

OBJECTIVE: Intraoperative detection of suboptimal coronary anastomoses allows revision before chest closure. We evaluated an epicardial 13-MHz ultrasound minitransducer as a means to detect three different coronary anastomosis construction errors. METHODS: In total, 120 internal thoracic artery-to-coronary artery anastomoses were constructed correctly (n = 60) or incorrectly (n = 60) with one technical error: suture crossover, purse-string or deep toe stitch (n = 20 each). Anastomoses were performed on ex vivo pressure-perfused porcine (96 anastomoses) and human hearts (24 anastomoses). Two blinded observers scanned and scored the anastomoses with epicardial ultrasonography. In 24 human and 24 porcine anastomoses, angiograms were made of 24 correct and 24 incorrect anastomoses and scored by two other blinded observers. Angioscopy and cast injection served as a reference. RESULTS: Overall, 119 of 120 anastomoses were accurately scored as correct or incorrect within a median of 67 seconds (8-381 seconds) by both observers (sensitivity 0.98, specificity 1.00, kappa 1.00 (1.00, 1.00, and 1.00 in angiography subset, respectively). One deep toe stitch that induced outflow corner stenosis was spotted by both observers but regarded as insignificant and thus inaccurately scored as correct. In 5 anastomoses, unintended irregularities were detected. By angiography, anastomoses were accurately scored with a sensitivity of 0.75 and a specificity of 0.81 ( P < .001 vs ultrasonography) and kappa of 0.54. Angioscopy and cast confirmed ultrasonographic findings and did not reveal irregularities other than detected by ultrasonography. CONCLUSION: Ex vivo epicardial 13-MHz ultrasonography allowed rapid and accurate evaluation of coronary anastomoses and detected technical construction errors with higher sensitivity and specificity than angiography.

Quality assessment of distal S(2)AS connector anastomosis by 13 MHz epicardial ultrasound.

OBJECTIVE: During application of a distal coronary bypass connector, we employed 13 MHz epicardial ultrasound to evaluate quantitative caliper measurements for vessel size matching and to assess anastomosis quality after connector deployment. METHODS: Two S(2)AS connector anastomoses were constructed on ex vivo pressure-perfused porcine hearts. Epicardial ultrasound measurements of the connector ring and anastomosis were compared to intravascular ultrasound measurement and cast dimensions. In 21 pigs, anastomotic sites with internal diameter of 2.25-3.0mm (internal mammary artery, IMA) and 1.8-2.2mm (left anterior descending coronary artery, LAD) were selected using external caliper and epicardial ultrasound measurements. Anastomoses were visualized and assessed intraoperatively (beating heart, n=21) and at 3 and 6 months' follow-up (explanted heart, n=10 each). RESULTS: Epicardial ultrasound underestimated connector dimension by < or =5% versus intravascular ultrasound and deviated < or =13% from cast dimensions for other anastomotic measurements. Caliper estimates of internal IMA and LAD diameter differed from ultrasound by -3+/-6% and -2+/-7% (mean+/-SD), respectively. Intraoperatively, the anastomotic orifice was flawless in all animals. It remained fully patent at 3 and 6 months by ultrasound, which was confirmed by histology. The connector to LAD percentage diameter stenosis changed from -12+/-5% intraoperatively to -1+/-7% at 3 months and from -5+/-6% intraoperatively to -16+/-13% at 6 months, in the growing pig model. CONCLUSIONS: In the pig, external caliper measurements provided a reliable quantitative estimate of inner graft and coronary diameter for connector size matching. Epicardial 13 MHz ultrasound is a promising method to assess coronary anastomosis quality even when connector metal is present.

The "Spacemaker", a New Device for Minimally Invasive Cardiothoracic Surgery: An Evaluation and Feasibility Study.

OBJECTIVE: Our aim was to evaluate a new inflatable lung retractor, the "Spacemaker", and its efficacy in facilitating minimally invasive cardiothoracic surgery without the need of one lung ventilation or carbon dioxide overpressure insufflation. METHODS: The device was tested in 12 anesthetized pigs (90-100 kg) placed on standard endotracheal ventilation. The device was introduced into the right or left side of the chest, depending on the intended procedure to be performed, via a 3-cm incision in the fifth intercostal space. A total of seven animals were used to evaluate hemodynamic and respiratory response to the device, whereas another five animals were used to assess the feasibility of a variety of minimally invasive cardiothoracic surgical procedures. RESULTS: Introduction was easy and unhindered. The device was inflated up to 0.6 bar, thereby pushing the lung tissue gently away cranially, posteriorly, and caudally without interfering with pulmonary function or resulting in respiratory compromise. In addition, hemodynamics remained stable throughout the experiments. Different closed-chest surgical procedures such as left atrial appendage exclusion, pulmonary vein exposure, pacemaker lead placement, and endoscopic stabilization for coronary surgery, were successfully performed. Removal was quick and complete in all cases, and lung tissue showed no remnant atelectasis. CONCLUSIONS: The "Spacemaker" may represent a reliable alternative to current conventional techniques to facilitate minimally invasive cardiothoracic surgery. Further research is warranted to confirm the effectiveness and the safety of this device and to optimize the model before its use in humans and its introduction into clinical practice.

In Vitro Hemocompatibility Testing of Dyneema Purity Fibers in Blood Contact.

OBJECTIVE: Heart valve and vascular prosthesis implantation is a common procedure for patients with heart valve stenosis or regurgitation and dilated or obstructive vascular disease. Drawbacks of conventional valve prostheses are the requirement for anticoagulant drugs, moderate durability, and suboptimal resistance to fatigue and tear. Dyneema Purity fibers are made from ultra-high-molecular-weight polyethylene filaments and are very thin, flexible, and fatigue and abrasion resistant and have high strength. Therefore, prostheses made from Dyneema Purity fibers might be attractive for use in the minimally invasive treatment of valvular- and vascular diseases. The aim of this study was to test the hemocompatibility of Dyneema Purity fibers in contact with blood. METHODS: Real-time platelet adhesion in human blood of 3 volunteers was quantified after 5 minutes of perfusion on single filaments (Ø 15 µm) of Dyneema Purity and polyester fibers. Plasma thrombin generation was measured by fluoroscopy for patches of Dyneema Purity fibers and for 5 commonly used polyester and expanded polytetrafluoroethylene cardiovascular prostheses. RESULTS: Platelet adhesion per 1 mm was 6 ± 1.4 on Dyneema Purity filaments and 15 ± 3.4 on polyester filaments (P = 0.02). Total formed thrombin and the time to peak of its maximum were noninferior for patches of Dyneema Purity fibers compared with the reference materials. CONCLUSIONS: Dyneema Purity fibers are noninferior in adhesion and coagulation activation compared with commonly used cardiovascular prostheses.

Myocardial blood supply through a direct left ventricle-coronary artery shunt is not aided by augmented coronary capacitance.

OBJECTIVES: Left ventricle-coronary artery shunting is proposed as an alternative means of myocardial revascularization when standard methods are not an option. During diastole, however, regurgitant coronary flow to the left ventricle decreases the efficacy of the left ventricle-coronary artery shunt. We investigated whether augmented coronary compliance would improve net forward shunt flow. METHODS: In 11 anesthetized pigs a specially designed stent was placed through the lateral wall of the left ventricle. Through an arterial graft, it was connected to the proximal left anterior descending coronary artery. A blind stump of the right internal thoracic artery (15 cm) was anastomosed to the distal left anterior descending coronary artery to serve as added coronary compliance chamber. Blood flow was measured in the coronary artery just distal from the left ventricle-coronary artery shunt, as well as in the shunt and in the compliance chamber entrance-exit. RESULTS: The left ventricle-coronary artery shunt decreased the net forward midcoronary flow to 53% +/- 18% (mean +/- SD) of native flow (8 +/- 4 vs 16 +/- 5 mL/min at baseline, P <.01). The augmented compliance did not significantly increase net forward coronary flow (61% +/- 25% of native flow, P <.01 vs baseline and P =.21 vs left ventricle-coronary artery shunt with normal compliance). The increase in systolic forward flow (53 +/- 23 vs 37 +/- 19 mL/min with normal compliance) was accompanied by a similar increase in diastolic regurgitant flow (-26 +/- 20 vs -16 +/- 16 mL/min). CONCLUSION: In healthy pigs a left ventricle-coronary artery shunt decreased net forward coronary flow to 53% +/- 18% of native flow. Augmentation of coronary artery compliance did not improve shunt performance.